Mobile communication systems employing a 2nd Generation (2G) Code Division Multiple Access (CDMA) scheme generally provide voice-based services over a relatively low-speed traffic channel on a forward and reverse link. Herein, the forward link is defined as a direction from a base station (BS) to a mobile station (MS), and the reverse link is defined as a direction from the mobile station to the base station. However, instead of the simple voice-based services, users now demand a variety of services. To satisfy such user demands, systems capable of providing data services have been developed, and a worldwide standard has been prepared. As described above, the mobile communication systems have recently evolved from voice-based systems to 3rd Generation (3G) systems which are designed to provide high-speed data services.
In the aforementioned mobile communication system, the mobile station and the base station occupy wireless channel resources to communicate with each other. Therefore, when all assignable wireless resources are currently in use, the base station can neither assign a new call nor increase a data transfer rate of an existing call. In other words, when the base station assigns a new call using more than the assignable amount of wireless resources or when the base station increases the data transfer rate of an existing call, not only the base station but also the mobile stations existing within a coverage of a neighboring base station are significantly affected. In addition, even if the call is not assigned or the data transfer rate is not increased, the amount of assignable wireless resources may change due to a fading effect or the like, thereby adversely affecting the system. Therefore, there is a need for a method for allowing a base station to accurately recognize an occupation state of wireless resources currently being used and for determining a desired data transfer rate.
In a technique for determining a data transfer rate on a reverse link, that is, determining a reverse link load, a total sector load is determined, a load caused by a mobile station which wants to determine a data transfer rate (hereinafter, such a mobile station (MS) will be referred to as a “target MS”) is then subtracted from the sector load, and the data transfer rate of the target mobile station is then regulated in a range where the sector load does not exceed a threshold. The currently used technique for determining the reverse link load is classified into two methods according to a manner of determining the sector load.
The first method is a load-based method in which only a load associated with a self sector user is determined as a sector load. The second method is a Rise Over Thermal (ROT)-based method in which all interferences including not only a self sector but also an external sector are taken into account in the sector load. Now, a process of controlling a data transfer rate on a reverse link according to the two method of measuring loads will be described in detail with reference to the accompanying drawings.
FIG. 1 is a flowchart illustrating a process in which a base station (BS) determines a data transfer rate on a reverse link by using a load-based method in a conventional mobile communication system.
Referring to FIG. 1, the BS measures loads (Loaduser) of all mobile stations (or users) in step 101. Herein, the load is defined as a ratio of a received power for a mobile station (MS) channel to a total received power in the BS. After measuring the loads of the MSs, the BS sums the loads (Loaduser) of the MSs in step 103, and thus determines a sector load (Loadsector). Thereafter, in step 105, the BS subtracts the target MS load (LoaduserT) from the sector load (Loadsector), and thus determines a reference load (Loadother). Then, in step 107, the BS determines a target MS's temporary data transfer rate (RateuserT,new) to be a minimum data transfer rate (RateMin).
After determining the temporary data transfer rate, in step 109, the BS computes a temporary load (LoaduserT,new) resulting from the target MS's temporary data transfer rate (RateuserT,new), sums the temporary load (LoaduserT,new) and the reference load (Loadother), and compares the summation value with a predetermined sector threshold load (Loadth).
If the comparison result shows that the summation value is greater than or equal to the predetermined sector threshold load, in step 111, the BS compares the temporary data transfer rate (RateuserT,new) with the minimum data transfer rate (RateMin). If the temporary data transfer rate (RateuserT,new) is greater than the minimum data transfer rate (RateMin), in step 113, the BS decreases the temporary data transfer rate (RateuserT,new) by one level. On the other hand, if the minimum data transfer rate (RateMin) is greater than or equal to the temporary data transfer rate (RateuserT,new), in step 115, the BS determines a target MS's data transfer rate to be the temporary data transfer rate (RateuserT,new), and transmits data transfer rate information to the target MS.
If the comparison result of step 109 shows that the sector threshold load (Loadth) is greater than the summation value, in step 117, the BS compares a maximum data transfer rate (RateMax) with the temporary data transfer rate (RateuserT,new). If the maximum data transfer rate (RateMax) is greater than the temporary data transfer rate (RateuserT,new), in step 119, the BS increases the temporary data transfer rate (RateuserT,new) by one level. Then, the procedure returns to step 109. On the other hand, if the temporary data transfer rate (RateuserT,new) is greater than or equal to the maximum data transfer rate (RateMax), in step 121, the BS determines the temporary data transfer rate (RateuserT,new) to be the maximum data transfer rate (RateMax).
In step 115, the BS determines the target MS's data transfer rate to be the temporary data transfer rate (RateuserT,new), and transmits the data transfer rate information to the target MS.
FIG. 2 is a flowchart illustrating a process in which a base station (BS) determines a data transfer rate on a reverse link by using an ROT-based method in a conventional mobile communication system.
Referring to FIG. 2, the BS measures an ROT and loads (Loaduser) of all mobile stations in step 201. Herein, the load is defined as a ratio of a received power for a mobile station (MS) channel to a total received power in the BS.
After measuring the loads of the MSs, in step 203, the BS determines a sector load (Loadsector) by using the ROT. In step 205, the BS subtracts a target MS's load (LoaduserT) from the sector load (Loadsector), and thus determines a reference load (Loadother). In step 207, the BS determines a target MS's temporary data transfer rate (RateuserT,new) to be a minimum data transfer rate (RateMin).
After determining the temporary data transfer rate, in step 209, the BS computes a temporary load (LoaduserT,new) resulting from the target MS's temporary data transfer rate (RateuserT,new), sums the temporary load (LoaduserT,new) and a reference load (Loadother), and compares the summation value with a predetermined sector threshold load (Loadth).
If the comparison result shows that the summation value is greater than or equal to the predetermined sector threshold load (Loadth), in step 211, the BS compares the temporary data transfer rate (RateuserT,new) with the minimum data transfer rate (RateMin). If the temporary data transfer rate (RateuserT,new) is greater than the minimum data transfer rate (RateMin), in step 213, the BS decreases the temporary data transfer rate (RateuserT,new) by one level. On the other hand, if the minimum data transfer rate (RateMin) is greater than or equal to the temporary data transfer rate (RateuserT,new), in step 215, the BS determines target MS's data transfer rate to be the temporary data transfer rate (RateuserT,new), and transmits data transfer rate information to the target MS.
If the comparison result of step 209 shows that the sector threshold load (Loadth) is greater than the summation value, in step 217, the BS compares a maximum data transfer rate (RateMax) with the temporary data transfer rate (RateuserT,new). If the maximum data transfer rate (RateMax) is greater than the temporary data transfer rate (RateuserT,new), in step 219, the BS increases the temporary data transfer rate (RateuserT,new) by one level. Then, the procedure returns to step 209. On the other hand, if the temporary data transfer rate (RateuserT,new) is greater than or equal to the maximum data transfer rate (RateMax), in step 221, the BS determines the temporary data transfer rate (RateuserT,new) to be the maximum data transfer rate (RateMax).
In step 215, the BS determines the target MS's data transfer rate to be the temporary data transfer rate (RateuserT,new), and transmits the data transfer rate information to the target MS.
As described above, the data transfer rate on the reverse link can be determined in the mobile communication system by using the load-based or ROT-based method. However, when the load-based method is used, interference caused by an external sector cannot be measured. As a result, a significant discrepancy may occur between a predicted sector load and an actual sector load. Thus, there is a need to determine a threshold of the sector load conservatively. Although the interference caused by the external sector is taken into account in the ROT-based method, a discrepancy between the predicted sector load and the actual sector load still exists.
In other words, the aforementioned two methods do not consider a phenomenon in which, when a data transfer rate of an MS included in a self sector increases, interference to an adjacent sector increases due to the MS having the increased data transfer rate, and thus transmission power increases in the adjacent sector, thereby increasing interference to the self sector. Likewise, when the data transfer rate of the MS included in the self sector decreases, decrease of interference from the external sector is not considered. Therefore, there is a problem in that a Quality of Service (QoS) deteriorates and wireless resources are wasted when inaccurate prediction of a sector load on a reverse link adversely affects an external sector or disables the use of remaining wireless resources.